Central Complex
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Central complex structure

The central complex is a prominent protocerebral neuropil that spans over the midline into both hemispheres. Its main component is the central body with an upper and lower division. The division are joined by two small neuropils structures, the noduli. The central complex includes another mid-line neuropil structure, the protocerebral bridge. In Diptera (such as the fruit fly), the upper division is called fan-shaped body and the lower division ellipsoid body（Hanesch et al., 1989; Young et al., 2009).

Properties of the central complex

Polarisation sensitivity
In the locust, about 20% of the central complex neurons have beens shown to display polarisation sensitive responses to light. In particular neurons of the lower division of the central body show polarisation sensitivity. The lower division appears to be less developed in insects that do not have polarisation vision.

Role in visual learning
In the fruit fly, it has been suggested that the central body is involved in visual learning, in particular, the fan-shaped body is thought to be important for learning spatial patterns of visual stimuli [Liu et al., 2006]．In navigation tasks with visual cues, the ellipsoid body appears to be important [Neuser et al., 2008]．

Generation of courtship song
Block of neurotransmission though acetylcholine or NO in the central body leads to impairments of courtship song generation in crickets. Thus, the central body is implied to be a crucial element in the generation of the courtship song pattern [Hoffmann et al., 2007; Weinrich et al., 2008]．

Integrative properties
Many neurons of the central complex are multimodal and can display complex event-related activities [Homberg 1985; 1994]．The central complex can thus be viewed as an important structure for the integration of information in the insect brain.

Dispositions of central complex neurons

The cytoarchitecture of the central complex has been most intensively studied in flies (in particular Drosophila) and in locusts (Locusta, Schistocerca).

Tangential cells
Tangential neurons are the primary input neurons of the central complex. The innervate various areas of the adjacent protocerebrum including the posterior optic tubercle and lateral accessory lobe and many, if not all columns of the central body or subdivisions of the protocerebral bridge.

Columnar cells
Columnar cells are the main output elements of the central body and their morphology can be used to divide the central body into distict columns innervated by these neurons. The columnar cells make topographically arranged connections between the left and right sides of the central body. Projection targets are the noduli and the lateral accessory lobes.

Pontine cells
Pontine cells make topographically arranged connections between the left and right sides of the upper division of the central body, in some cases in different layers．


References

Hanesch U, Fischbach KF, Heisenberg M (1989) Neuronal architecture of the central complex in Drosophila melanogaster. Cell Tissue Res 257:343-366.

Homberg U (1994) Flight-correlated activity changes in neurons of the lateral accessory lobes in the brain of the locust Schistocerca gregaria. J Comp Physiol A 175:597-610.

Liu G, Seiler H, When A, Zars T, Ito K, Wolf R, Heisenberg M, Liu L (2006) Distinct memory traces for two visual features in the Drosophila brain. Nature 439:551-556.

Neuser K, Triphan T, Mronz M, Poeck B, Strauss R (2008) Analysis of a spatial orientation memory in Drosophila. Nature 453:1244-1247.

Weinrich A, Kunst M, Wirmer A, Holstein GR, Heinrich R (2008) Suppression of grasshopper sound production by nitric oxide-releasing neurons of the central complex. J Comp Physiol A 194:763-776.

Young JM, Armstrong JD (2009) Structure of the adult central complex in Drosophila: Organization of distinct neuronal subsets. J Comp Neurol 518:1500-1524.